(i) Field of the Invention
The present invention relates generally to a rotary machine, and more specifically to a rotary type fluid machine.
(ii) Description of the Prior Art
The typical construction of a scroll-type compressor, for instance, generally known in art of the fluid compression machines as shown in FIG. 4, a schematic view showing the general principle of operation, is such that there are provided two scroll or spiral elements of an identical cross-sectional shape, one spiral element 2 being fixed in position onto the surface of a sealing end plate having a generally central delivery opening 4. Further to this construction, these two spiral elements are shifted in rotation relatively 180 degrees apart from each other and are also shifted in relative location by a distance 2 .rho. (=the pitch of a spiral pattern-2.times.thickness of a spiral element plate) so as to be nested in position with each other in such a manner as schematically shown in the figure that they may be located in their relative position to come in contact with each other at four points 51, 52 and 51', 52'. According to this construction, it is further noted that the one spiral element 2 is disposed stationary in position, and the other element 1 is arranged to move in revolution or in solar-orbital motion with a radius of .rho.=0, 0' about the center 0 of the spiral element 2, without moving in rotation or in planetary motion on its own axis, by using a crank mechanism having a radius .rho..
With such construction, there are defined small spaces or chambers 3, 3 being tightly enclosed extending along and between the abutting points 51, 52 and 51', 52' of the spiral elements 1, 2, respectively, the volumes of which chambers 3, 3 vary gradually in continuation with the solar or revolving motion of the spiral element 1.
Reviewing more specifically, it is notable that when the spiral element 1 is first caused to be revolved 90 degrees starting from the state shown in FIG. 4 (A), it turns to the position as shown in FIG. 4 (B), then when it is revolved 180 degrees, then it turns to the state as shown in FIG. 4 (C), and when it is further revolved 270 degrees, it turns then to the state as shown in FIG. 4 (D). As the spiral element 1 moves along in revolution, the volumes of the small chambers 3, 3 decrease gradually in continuation, and eventually, these chambers come in communication with each other and merge into one tightly enclosed small chamber 53. Now, when it moves in revolution further 90 degrees from the state shown in FIG. 4 (D), it turns back to the position as shown in FIG. 4 (A), and the small chamber 53 would then be caused to be reduced in its volume as it turns from the state shown in FIG. 4 (B) to that shown in FIG. 4 (C), and eventually it would turn to a smallest volume intermediate the states shown in FIGS. 4 (C) and (D). During this stage of motion in revolution, outer spaces starting to be opened as seen in FIG. 4 (B) grow as the element 1 turns along from the state of FIG. 4 (C) through the state of FIG. 4 (D) to the state of FIG. 4 (A), thus introducing another volume of fresh air from these outer spaces into the tightly enclosed small chamber to be eventually merged together, and then repeating this cycle of revolutional motion so that the gas thus-taken into the outer spaces of the spiral elements may accordingly be compressed, thus being delivered out of the delivery opening 4.
The foregoing description is concerned with the general principle of operation of the scroll-type compressor, and now, referring more concretely to the construction of this scroll-type compressor by way of FIG. 5 showing in longitudinal cross-section the general construction of the compressor, it is seen that a housing 10 is comprised of a front end plate 11, a rear end plate 12 and a cylinder plate 13. The rear end plate 12 is provided with an intake port 14 and a delivery port 15 extending outwardly therefrom, and further installed securely with a stationary scroll member 25 comprising a spiral or helical fin 252 and a disc 251. The front end plate 11 is adapted to pivotally mount a spindle 17 having a crank pin 23. As typically shown in FIG. 6 which is a transversal cross-sectional view taken along the plane defined by the arrow VI--VI in FIG. 5, in operative relationship with the crank pin 23 there is seen provided a revolving scroll member 24 including a spiral element 242 and a disc 241, through a revolving mechanism, which comprises a radial needle bearing 26, a boss 243 of the revolving scroll member 24, a square sleeve member 271, a slider element 291, a ring member 292 and a stopper lug 293 and the like.
According to the general construction of this scroll type compressor, it is generally designed that the small volume chamber 53 would gradually reduce in its volume as the revolving element rotates in revolutionary motion, thus having the fluid under pressure delivered out of its delivery port. With the existing thickness of the spiral elements involved therein, however, it is inevitable that the volume of the small chamber could not be made nullified at all, thus resulting in the so-called top clearance volume left unnullified. In this connection, it is notable that the fluid remaining under pressure in the this top clearance volume would then be held from being delivered out of the delivery port 4, which would possibly be turned to be led back to the small chambers 3, 3, after all. As a consequence, it is to be noted that the extent of work done by the compression machine upon the fluid left in the top clearance volume would then turn out to be a loss of work, accordingly.
In the attempt to cope with such drawback as noted above, there has been proposed the rotary type fluid machine which is equipped with the scroll or spiral elements of the construction as typically shown in FIG. 7 under the Japanese patent application No. 206,088/1982.
Referring more specifically to this construction, there is shown the stationary spiral element designated at the reference numeral 501, wherein the curves of the radially outer and inner surfaces of the spiral element 501 are designated at 601 and 602, respectively. It is seen that the radially outer curve 601 is defined as an involute curve having the base circle radius b and the starting point A, the curve section E-F of the radially inner curve 602 is an involute curve having the shift in phase of (.pi.-.rho./b) with respect to the radially outer curve 601, and the curve section D-E is an arc having the radius R. Also, the connection curve at 603 for connecting the radially outer and inner curves 601 and 602 is an arc having the radius r. The point A is the starting point of the outer curve 601 in the involute curve, and the point B is the boundary point between the outer curve 601 and the connection curve 603, where the both curves share the same tangential line. The point C is the one that is defined sufficiently outside of the radially outer curve 601, and the point D is the boundary point between the inner curves 602 and the connection curve 603, at which point there are two arcs having the radii R and r in osculating relationship with each other. The point E is the boundary point between the arc section (D-E) of the radially inner curve 602 and the involute curve section E-F, where the both curves share the same tangential line. The point F is the one which exists sufficiently outside of the inner curve 602.
It is noted that the other revolving spiral element 502 is in the identical construction.
Now, the radii R and r may be given with the following equations; that is EQU R=.rho.+b.beta.+d (1) EQU r=b.beta.+d (2)
where,
.rho. is the radius of revolutionary motion; PA1 b is the radius of a base circle ##EQU1## .beta. is a parameter. PA1 b is the radius of a base circle of said involute curve.
The parameter .beta. is equal to an angle defined by a straight line segment passing the origin 0 and the X-axis in the negative quadrant. Two points of intersection of the straight line segment passing the origin 0 and at the angle of .beta. and the base circle are seen existing in the line segments EO.sub.2 and BO.sub.1. It is also seen that the straight line segments EO.sub.2 and BO.sub.1 extend in osculation with the base circle at the points of intersection noted above.
More specifically, it is noted that the parameter .beta. is defined to be a given marginal condition for the establishment of the involute curve for the radially outer and inner curves in the configuration of the spiral element, and conversely that this parameter .beta. would eventually define the marginal points E and B for the attainment of a due involute curve.
However, according to the compression machine which incorporates the scroll or spiral elements 252 and 242 having the configuration as noted hereinbefore, it has sometimes been experienced that when in a high load operation in which there exists generally a substantial difference in pressures as found between the low pressure side and the high pressure side of the machine, since the rigidity or stiffness of the radially inner leading end of the spiral element as shown by an arrow in FIG. 4 (A) is relatively smaller than that at other portions, there is a high possibility that this particular leading end would turn to be broken during the operation.
For this reason, it is notable that the height of the spiral element would be restricted from being designed to be too large. In this respect, therefore, it is the practice in the design engineering of a large displacement machine that the radius of the base circle b or the radius of revolutionary motion .rho., in place of the height, of the spiral element be designed to be greater, thus resulting in an increased overall outer diameter of the spiral element, accordingly. This would, however, be inconvenient in view of the compactness and handling of the rotary machine.